There is a need for improved methods and materials which extend the current knowledge and applications to create practical, cost-effective solutions for the security field. Security of currency, identification documents, product brands, and other materials has become an increasingly important concern for government and industry. As theft and fraud increase, security protocols must evolve to detect and prevent the increasingly more sophisticated and technologically based methods of counterfeiting and product diversion.
While there are many different methods and techniques used to provide security, an approach that uses more than one type of security is preferable. In such an approach, multiple security discrimination features are examined.
If one or more of the individual features is compromised, the security of the system as a whole remains intact. Such methods using multiple discrimination features are taught, for example, in U.S. Pat. No. 5,418,855 to Liang et al., assigned to the same assignee as the present invention.
The use of fluorescent materials such as ultraviolet (UV)-fluorescent, infrared (IR)-fluorescent, or near-infrared (NIR)-fluorescent materials for security markings is well known. The use of fluorescent materials allows the user to easily detect the security markings by irradiation of the marks with a suitable UV or NIR/IR light source. The fact that fluorescent materials emitting light in the visible spectrum can be detected by simple examination has made them easier to counterfeit and/or duplicate. However, this fact is also an advantage in that the user can easily and quickly authenticate the security marks.
While there are important distinctions between the uses of UV-fluorescent and IR-fluorescent materials that emit in the IR (infrared) and/or NIR (near-infrared) range, there are also advantages and disadvantages in the use and applicability of the latter materials, e.g., the NIR/IR emissions are not detectable by simple visual observation. As with UV fluorescence, this can be advantageous for some applications, but disadvantageous for other applications.
Many fluorescent materials are also easily detectable under illumination in the visible portion of the spectrum, but “invisible” fluorescent materials are known, i.e., those materials that are not visually detectable under ordinary white-light, but emit detectable fluorescent light when illuminated by light outside the visible spectrum.
Inkjet printing is a versatile technique in that it can deliver small volumes of liquid inks with a variety of different compositions that can be specifically formulated for many different applications. Inkjet printing methods have been used successfully to print on a variety of different substrates, including many types of paper, from cardboard to newsprint, many types of fabric, and various other polymers, such as plastic. These characteristics make inkjet printing an excellent method of delivery for many types of materials, including fluorescent indicia for security marking. Color inkjet printers, however, typically use sets of subtractive-color inks (typically 3-6 inks in a set), combined in accordance with a corresponding color space. Such inks are generally not fluorescent and are intended to be visible under ordinary white-light illumination (illumination in the visible portion of the spectrum, having wavelengths generally in the range between 400 nm and 700 nm).
While fluorescent security indicia have been widely used in currency and in passports and other identification documents, most of such applications have used single fluorescent colors or simple combinations of individual colors, which have often been visible under ordinary white-light illumination. Thus, security applications using such fluorescent materials may not provide the level of security desired for certain applications.
The foregoing shortcomings and problems of the prior art are improved upon, and further advantageous solutions are provided by the present invention.